The present invention relates to systems that rely on suction for brewing beverages; for example, vacuum coffee makers.
Beverages such as tea and coffee which rely on steeping and/or brewing to extract flavor from leaves or grounds are popular and prevalent. There are many different systems and many techniques for brewing, producing varying results in texture and flavor. Many of these systems (for example vacuum coffee makers) rely on suction in the brewing process.
In a vacuum coffee maker there are typically two containers, one above the other, with a tube extending down from the bottom of the upper container to the lower container. A filter is placed at the top of the tube and dry coffee grounds are placed on the filter. The lower container is filled with water and the two containers are fitted together such that a seal is formed.
A heating element, either integrally formed with the lower container or placed beneath the lower container, heats the water in the lower container. As the water boils and expands, water and water vapor (steam) are forced up the tube, past the filter, and into the upper container, mixing with the coffee grounds. When the water in the lower container has nearly completely evaporated, the heating element shuts off or current to the heating element is reduced, causing the temperature in the lower container to cool and the pressure to drop, creating suction and drawing water through the filter and into the lower container. The upper container is removed and the coffee is served from the lower container.
There are advantages to brewing systems that rely on suction. Coffee brewed using a vacuum coffee machine is often considered full-bodied without heavy sediment. Water can be poured into a lower container rather than into the upper container. But there are disadvantages as well. For example, the flow of the water up the tube, especially when only a small quantity of water remains in the lower container, can become erratic due to formation of steam bubbles from the heater surface. This leads to intermittent pressurized flow of water upwards through the tube, especially towards the end of the heating cycle. Also, the vacuum coffee machine cannot be used in a compact vertical space. To remove the lower container for serving, the vacuum coffee machine must be disassembled. In order to remove the lower container, the tube must be separated from the lower container. To separate the tube from the lower container, the seal between the upper and lower chambers must be broken and the upper chamber vertically separated from the filter and tube.